Why Do Acromial Fractures Occur After Reverse Shoulder Arthroplasty?

Acromial fracture is a known complication of reverse shoulder arthroplasty, and it is often associated with poor clinical outcomes.

Multiple mechanisms have been proposed as the cause of these fractures. A drawback of previous research, however, is that study authors have combined all types of acromial fractures (ie, all Levy types) into a single “fracture” group. This fails to take into account differences in the fractures based on anatomic location, making it difficult to pinpoint potential causes of each fracture type.

In addition, few studies have evaluated clinical outcomes of acromial fractures through the lens of fracture location and displacement. Non-operative management is associated with poor fracture union rates; however, little is known about effective management strategies for these fractures.

A new retrospective, multicenter study, published online ahead of print by the Journal of Shoulder and Elbow Surgeons, takes on both issues by evaluating:

  • The relationship between acromial morphology and fracture location (Levy type I vs. Levy type II)
  • The impact of fracture location and displacement on clinical outcomes

Study Methodology

For the study, the researchers identified 87 patients who had developed an acromial fracture after undergoing reverse shoulder arthroplasty at their 3 institutions between January 2004 and July 2018.

Applying the study’s exclusion criteria left the researchers with 42 patients for the first part of the study: radiographic evaluation of acromial morphology. These patients were divided into 2 groups:

  • Levy type I fractures (n=17)
  • Levy type II fractures (n=25)

Patients with Levy type III fractures were excluded because these fractures involve the scapular spine and the researchers wanted to focus on acromial fractures (Levy type I and Levy type II).

Twenty-two patients had been followed for at least 2 years and were, therefore, available for the second part of the study: evaluation of clinical outcomes. They were stratified into 2 groups according to their pre- and postoperative ASES scores:

  • Those in the good outcome group had at least 20-point improvement in the ASES score, indicating they’d achieved the minimal clinically important difference (MCID).
  • Those in the poor outcome group did not achieve the MCID.

The 2 groups were compared clinically and radiographically. Radiographic comparisons included fracture location and displacement, the latter of which was based on acromiohumeral distance (AHD), acromion-glenosphere distance (AGD), and acromion-cup distance (ACD) (Figure 1).

Figure 1. Radiographic measurements: The acromion-glenosphere distance, measured on a scapular Y-view (A), and the acromion-cup distance (B).

Study Findings

The study authors reported the following findings:

  • Levy type 1 fractures more commonly occurred in the coronal plane (94%) and had a transverse pattern, while Levy type II fractures were more likely to be found in the sagittal plane (88%) and had an oblique pattern. (Figure 2).

Figure 2. Scapular Y-view radiographs demonstrating transverse Levy I fracture pattern (A,C). Grashey radiographs demonstrating oblique Levy II fracture pattern (B,D).

  • Levy type I fractures had a significantly greater acromial slope than Levy II fractures (127° vs 117°; P<0.001), as well as a higher posterior acromial slope (136° vs 130°; P=0.03).
  • The association between an increased acromial-spine angle and Levy type was not statistically significance (83° vs 75°; P=0.064).
  • Of the 22 patients with at least 2 years of clinical and radiographic follow-up, 12 patients (55%) achieved the MCID.
  • Patients who achieved the MCID has significantly less pain, with an average VAS score of 1 compared with 6 for patients who did not achieve the MCID. They also had more improvement in forward flexion and external rotation at final follow-up.
  • Patients who were unable to achieve the MCID had acromial fractures with greater displacement, as indicated by the significantly lower AHD, ACD, and AGD values. (Figure 3).

Figure 3. Radiograph of a patient who did not achieve the MCID, demonstrating a more displaced fracture (A) compared with a less displaced fracture in a patient who achieved the MCID (B).

  • The number of patients who achieved the MCID was similar between the Levy type I and Levy type II groups (P=0.093).

“An increased acromial slope is associated with transverse fractures in the Levy type I region, whereas a lower acromial slope is associated with oblique fractures in the Levy type II region,” the researchers said. They also concluded that most patients (55%) with acromial fractures achieve the ASES MCID at mid-term follow-up and those who did not achieve the MCID had more displaced fractures.

Study Implications

The researchers noted that previous studies have found that an increase in acromial stress, resulting from an increase in deltoid tension, puts patients at higher risk for fracture. They had hypothesized, based on these earlier findings, that differences in the acromial slope could alter deltoid fracture and impact the pattern of the fracture.

“This was supported by our results,” the researchers said, “given that a higher acromial slope (vertically oriented) was associated with Levy type I fractures whereas a lower slope horizontally oriented) was correlated with Levy type II fractures.”

They further described possible mechanisms for these fractures, noting that “[f]ractures in the Levy I region had a transverse pattern, suggesting a tension mechanism due to deltoid pull, resulting in avulsion of the anterior acromion, whereas Levy type II fractures appeared to be oblique, suggesting impaction that may be due to impingement of the greater tuberosity on the lateral aspect of the acromion.”

They also noted that preoperatively, all patients had a superiorly migrated humeral head engaging the acromion. They theorized that “this finding sheds light on the fact that these fractures occur partly as a result of the weakening of the acromion by the articulating humeral head, which may lower the incidence threshold of these fractures.”

They recommend, based on their findings, that surgeons:

  • Minimize over-tensioning in patients with a more vertical acromion. This can be achieved by utilizing an inlay-varus humeral stem and avoiding smaller humeral head cuts.
  • Minimize impingement between the greater tuberosity and the acromion in patients with a more horizontal acromion. The researchers recommend using 3D software during preoperative planning and selecting an implant that will reduce impingement at the acromion-greater tuberosity connection.

In addition, the researchers suggested that surgeons consider additional interventions, including surgical reduction and fracture fixation, in patients with more severely displaced fractures, as the study findings confirmed their hypothesis that patients with greater fracture displacement would have worse outcomes.


Haidamous G, Merimee S, Simon P, Denard PJ, Lädermann A, Mighell MA, Gorman RA 2nd, Frankle MA. Acromial fractures following reverse shoulder arthroplasty: the role of the acromial morphology and a comparison of clinical outcomes. J Shoulder Elbow Surg. 2022 Feb 18;S1058-2746(22)00226-9. doi: 10.1016/j.jse.2022.01.132. Online ahead of print.

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